A touchscreen panel is an input device normally layered on the top of an electronic visual display of an information processing system, which is common in devices such as game consoles, personal computers, tablet computers, electronic voting machines, and smartphones. They can also be attached to computers or, as terminals, to networks. A user can give input or control the information processing system through simple or multi-touch gestures by touching the screen with a special stylus/pen and/or one or more fingers.
There are variety of touchscreen technologies with different methods of sensing touch, such as resistive touchscreen, surface acoustic wave touchscreen, capacitive touchscreen, and so on. Taking capacitive touchscreen as an example, touching the screen of the touchscreen panel results in a distortion of the screen's electrostatic field, measurable as a change in capacitance. Different known technologies may be used to determine the location of the touch, and the location is then sent to the touchscreen panel controller for processing. U.S. Pat. No. 4,853,498 A discloses a location determination method, where position measurement for capacitive touchscreen panel has conductive face plates and apparatus to generate an address signal indicative of styling contact location. The touchscreen panel according to U.S. Pat. No. 4,853,498 A provides a faceplate with an electrically conductive layer of a consistent resistivity employs a position measurement apparatus to generate an address signal indicative of a position on the faceplate in contact with a stylus. Position measurement signal is applied to a first pair of opposed electrodes and a second pair of opposed electrodes positioned along respective side margins of the faceplate. The resistivity of the conductive layer establishes effective resistances of Rx and Ry between the respective first and second pairs of electrodes. Position measurement subcircuits measure currents drawn through the electrodes whenever the stylus touches the conductive layer, thereby to form an address signal indicative of the location at which the stylus contacts the faceplate. The skilled person should understand that a distance between two touch points on the screen can be calculated using the address signals indicating the locations of such two touch points.
The touch technology trending towards more sensitive, higher resolution, more dimensions (i.e. 3D position measuring with orientations) make it suitable for position measuring in an industrial robot commissioning system. Compared with laser based or encoder based industrial 3D measuring device, touchscreen panel is easy accessible and low-cost.
The position measurement by use of touchscreen panel depends on the established effective resistance at the touch point on the touchscreen, and the distance between two touchpoints as calculated as above has an error as a result of influences of the misplacement of the sensing elements disposed between the touchpoints. Therefore, where the touch points are confined in a relatively small area of the screen, for example such as relatively small area encompasses sensing elements less than 10 in a direction, the error for the distance of their position measurements is small and thus can be ignored for a relatively high accurate position measurement. However, accuracy of the position measurement becomes unsatisfactory when it is applied to a relatively large area of the touchscreen, for example encompasses sensing elements more than 10 in a direction.
A coordinate measuring machine (CMM) can be used to calibrate the touchscreen coordinate system to reduce the position measurement error. However, this makes the industrial robot commissioning system more costly by introduction of extra device like CMM.